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Weight Loss and Diet Pills: Options to Know

Medically reviewed by Leigh Ann Anderson, PharmD. Last updated on June 8, 2021.

What Are Weight Loss Drugs?

Prescription weight loss pills, also called anti-obesity drugs or “diet pills”, are sometimes prescribed to a patient as an additional tool in the treatment for weight loss. Tools added to medication treatment typically also include a plan for lower fat and calorie foods, as well as a regular exercise program.

Most weight loss drugs that suppress the appetite are known as anorexiants. Some weight loss drugs contain a stimulant medication and are classified as controlled substances by the Drug Enforcement Agency (DEA).

Since 2012, the FDA has approved several new weight loss medicines, including:

In 2020, the FDA requested that the manufacturer withdraw lorcaserin (Belviq, Belviq XR) from the U.S. market as the risk of cancer (including pancreatic, lung and colorectal) outweighed any benefit from the drug.

Patients who are overweight or obese with any health condition should consult with their physician prior to beginning a weight loss or exercise program.

There are very few proven choices in over-the-counter (OTC) or nonprescription medications for effective weight loss. One agent that is available without a prescription is Alli (orlistat), a lower-dose version of the prescription drug Xenical.

Many people who are trying to lose weight may choose dietary supplements or herbal medications, but most of these products have not been adequately studied for effectiveness or safety. None are approved by the U.S. Food and Drug Administration (FDA) for weight loss. Check with a healthcare provider for advice before using herbal or dietary supplements for weight loss.

How Much Weight Can I Lose With Diet Pills?

Prescription weight loss drugs may be an option for patients who have serious health risks, such as high blood pressure, type 2 diabetes, or high cholesterol and cannot control their weight with diet and exercise alone. Weight loss drugs should not be used as a substitute for healthful eating and a regular exercise program.

Over one year, patients using weight loss drugs may lose roughly 5% to 10% of their initial weight when used as part of an effective diet and exercise plan. However, for most weight loss drugs, if you have not lost at least 5% of your initial body weight after 12 weeks, it is unlikely that you will achieve and sustain clinically meaningful weight loss with continued treatment.

Common "Diet Pills" or Weight Loss Drugs

Brand Name Generic Name Description Controlled Substance?

Adipex-P, Lomaira

phentermine oral tablet or capsules; appetite suppressant; anorectic yes, C- IV
Alli orlistat oral capsule; lipase inhibitor; inhibits fat absorption in the intestine available over-the-counter (OTC)
Belviq, Belviq XR (brands and generic discontinued) lorcaserin selective serotonin 2C receptor agonist; promotes a feeling of fullness or satiety; withdrawn from US market in 2020 due to increased cancer risk. product withdrawn
Bontril PDM  phendimetrazine oral tablets; appetite suppressant; anorectic yes, C-III
Desoxyn methamphetamine oral tablets; appetite suppressant; use cautiously if prescribed for weight loss due to high potential for abuse, illegal distribution yes, C-II
Didrex (brand discontinued) benzphetamine oral tablet; appetite suppressant; anorectic yes, C-III
Generic only diethylpropion oral tablet; appetite suppressant; anorectic yes, C-IV
Meridia sibutramine anorectic; withdrawn from US market in 2010 due to increased heart toxicity risk. product withdrawn
Qsymia phentermine and topiramate extended-release oral capsules; combination appetite suppressant-anorectic; exact action of topiramate on weight loss is not known yes, C-IV
Suprenza (brand discontinued) phentermine oral tablet; appetite suppressant; anorectic brand not available; generic C-IV
Xenical orlistat oral capsule; lipase inhibitor; prescription form of Alli (OTC); higher dose than Alli; inhibits fat absorption in the intestine not controlled; prescription required.
Contrave bupropion and naltrexone oral tablet; increases metabolism, suppresses appetite, affects central reward center (proposed mechanism) not controlled;  prescription required.
Saxenda liraglutide once-daily subcutaneous injection; glucagon-like peptide-1 (GLP-1) receptor agonist not controlled;  prescription required.
Wegovy semaglutide once-weekly subcutaneous injection; glucagon-like peptide-1 (GLP-1) receptor agonist not controlled; prescription required.

How Effective Are Weight Loss Drugs?

Weight loss drugs don't always work for everyone. It is usually recommended that one to two pounds of weight can be safely lost per week. Weight loss drugs typically result in a 5% to 10% weight loss over a 12-month period when used as part of a diet and exercise plan.

For a patient weighing 200 lbs, this would translate into losing about 10 to 20 pounds over one year, which would fall within the safe guidelines for weight loss. While this amount of weight loss seems small, it may be enough to help lower blood pressure or have a positive effect on blood sugar.

Results from the Wegovy clinical studies showed an average weight loss of 14.9% of body weight at 68-weeks vs. 2.4% for placebo. In a 200 lb patient, this would equate to almost 30 lbs lost at 68 weeks.

Who Should Use Weight Loss Drugs?

Generally, most people should initially try to lose weight using diet and exercise. Prescription diet pills are used in more severe circumstances, when weight loss has not been successful and the patient has important health risks associated with being overweight or obese. However, diet and exercise should always be used in conjunction with prescription weight loss drugs.

Most prescription weight loss drugs note in the package labeling that a person should meet certain requirements, such as a specified body mass index (BMI) or have a serious weight-related medical risk before using these drugs.

Weight loss drugs are usually indicated for obese patients with an initial body mass index (BMI) greater than 30 kg/m2 or overweight patients with a BMI greater than 27 kg/m2 in the presence of other risk factors (eg, high blood pressure, type 2 diabetes, high cholesterol).

Examples of serious medical risks include:

To help assess your health risk based on weight, calculate your body mass index (BMI) here.

Plentity for Weight Loss

In April 2019, the FDA approved Plenity to aid in weight management, in conjunction with diet and exercise, in overweight and obese adults with a Body Mass Index (BMI) of 25–40 kg/m2.

  • Plenity is an oral, non-systemic capsule that contains hydrogel particles that absorb water and expand in the stomach leading to a feeling of fullness.
  • In a placebo-controlled study of Plenity in 436 overweight or obese adults, the primary endpoint was achieved with 59% of adults in the treatment group achieving weight loss of 5% or greater after six months.
  • There were no statistical differences in side effects between treatment groups, which primarily included stomach side effects (fullness, bloating, flatulence, and/or abdominal pain).

Should I Try to Lose Weight If I Am Pregnant?

A certain amount of additional weight gain, and no weight loss, is currently recommended for all pregnant women, including those women already overweight or obese.

  • Weight loss drugs should not be used during pregnancy. All weight loss drugs are contraindicated (meaning do not use) in pregnancy.
  • Weight loss offers no potential benefit and may result in fetal harm during pregnancy.
  • Talk to your doctor about how much weight you should gain during pregnancy, and how quickly.
  • If you are taking a weight loss drug currently, speak with your doctor before trying to become pregnant, as you may need to stop your medicine for a period of time before pregnancy occurs.

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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.